Ink jet printing is generally a non-impact method for producing images by the deposition of ink droplets in a pixel-by-pixel manner to an image-recording element in response to digital signals.
The inks used in the various ink jet printers can be classified as either dye-based or pigment-based. A dye is a colorant, which is dissolved in the carrier medium. A pigment is a colorant that is insoluble in the carrier medium, but tends to be dispersed/suspended in the form of small particles, often stabilized against flocculation and settling by the use of dispersing agents. Pigment-based inks are generally considered to be less stable than dye-based inks. The carrier medium can be a liquid or a solid at room temperature in both cases. Commonly used carrier media include water, mixtures of water and organic co-solvents and high boiling organic solvents, such as hydrocarbons, esters, ketones, etc.
Plain paper is generally used to refer to paper that has not been specially coated or designed for specialty uses. Plain paper is generally composed of cellulose fibers and fillers. In many cases, fillers tend to be anistropic to the flow of ink and generally have little effect on wicking. However, when ink travels along and through cellulose fibers the flow tends to be directional, and, if a dye is deposited along the way, either through bonding at active sites or evaporation of the solvents, it is seen as wicking. Dye-based inks where the dye tends to penetrate into the paper and/or wick, tend to result in low optical density and/or ragged edges.
Pigment-based inks tend not to have the same problems as dye-base inks when printed on plain paper. Pigment-based inks have been formed which can create a high print quality (PQ) on plain paper. Due to the fact that pigment-based inks have been found to provide higher print quality than traditional dye-based inks, traditional wisdom has been that inks requiring a high print quality (typically black inks) should be pigment-based inks. One such high print quality pigment-based ink is sold by Hewlett Packard under the trade-name HP 56 black ink jet print cartridge for the Deskjet 5550, product # C6656AN.